1. Field
The present invention relates to a robot and a method of controlling walking thereof, and more particularly to a biped robot, which generates a stable walking pattern similar to that of a human while walking, and a method of controlling walking of the robot.
2. Description of the Related Art
In general, machines, which conduct motions similar to that of a human using an electric or magnetic action, are referred to as robots. Early robots were industrial robots, such as manipulators or transfer robots for the purpose of work automation and unmanned operation in production sites. Recently, a biped walking robot (hereinafter, referred to as a biped robot), which has a joint system similar that of a human and easily walks with two feet in human work and living spaces, has been researched and developed. U.S. Pat. Nos. 5,151,859 and 5,432,417 disclose examples of the above biped robot.
A walking pattern of a biped robot is generated through the following process. First, when a walking instruction, such as a walking speed, a number of steps, or a step width, is given, target positions and directions of both feet are determined and positions and direction trajectories of both feet according to time are generated based on the determined target positions and directions. Here, a target zero moment point (ZMP; specifying the point with respect to which dynamic reaction force at the contact of the foot with the ground does not produce any moment, i.e. the point where total inertia force equals zero) trajectory is determined also by the positions of both feet. A target ZMP is set such that the robot can stably walk using a principle that the robot does not fall down in case that the ZMP is located in a support polygon formed by one supporting foot or both feet when the robot walks, and a position of a torso of the robot is determined such that the ZMP of the robot is equal to the target ZMP. This position of the torso of the robot is obtained using a simplified robot model, and when the determined position of the torso is applied to a real robot, there is a difference between the target ZMP and the real ZMP. Thus, the walking pattern of the robot is generated by determining the position of the torso of the robot until this ZMP error is smaller than a random value, and positions/directions of both feet and the torso of the robot are controlled according to the walking pattern, thereby allowing the biped robot to walk.
However, the real ZMP differs from the target ZMP due to various differences of characteristics between a robot model and the real robot, and thus causes the walking of the robot to be unstable. The walking stability of the robot is badly influenced by unexpected contact or external force, and if severe, the robot may lose its balance and thus fall down. Therefore, in order to allow the robot to stably walk without falling down, a given walking pattern must be corrected in real time. Here, a real time stabilizer calculates a necessary position value (x, y) of the torso, and thus controls the stabilization of the robot such that the robot cannot fall down.
When a robot 1 walks through the above real time stabilization control, when a singularity pose is generated, it is difficult to achieve real time stabilization control. This singularity pose occurs when a relative distance between ankle joints 2 and hip joints 4 located at both side ends of the lower portion of a torso 3 is equal to the length of legs 5, as shown in FIG. 1. The real time stabilization control is method of changing the horizontal position value of the torso 3 in real time to prevent the robot 1 from falling down while walking. However, when the singularity pose is generated, the horizontal position value of the torso 3 cannot be changed. Conventionally, in order to avoid the singularity pose generating state, the height of the torso 3 is decreased from Zc to Zc−1. However, when the height of the torso 3 is decreased from Zc to Zc−1, the knees 6 must be severely bent, and thus the robot 1 has a walking pattern differing from that of a human, and thus does not accurately represent a human being.